In a WDM (Wavelength Division Multiplexing) network system, a transponder comprises an optical-to-electrical converter (O/E) that receives an optical signal and converts it to an electrical signal and an electrical-to-optical converter (E/O) that receives an electrical signal and converts it to an optical signal. A signal transferred to the transponder is subjected to the optical-to-electrical conversion and electrical-to-optical conversion. Because separate transponders have been used for transmission/reception and for regenerative repeating, the cost of a standby transponder is high. In addition, when an optical path failure occurs and the path must be switched, a bypass path used for switching must be located near enough to eliminate the need for regenerative repeating by an intermediate WDM apparatus (must be located relatively near).
Patent Document 1 discloses the configuration of an optical cross-connect apparatus having a wavelength conversion repeater capable of converting the wavelength of a signal to an arbitrary wavelength. This optical cross-connect apparatus, in which a standby wavelength conversion repeater is shared by multiple working paths, works as an apparatus having the failure recovery function via in-channel control at network failure time and variably controls the path switching and the usage wavelength setting according to an instruction from the network management apparatus.
Patent Document 2 discloses the configuration of a transponder in which an optical switch is provided between each transponder and a related transponder and the optical switch selectively terminates the signal from the related transponder or transfers the signal to the related transponder. Patent Document 3 discloses the configuration of a transponder that has both the transmission/reception function and the regenerative repeating function.    [Patent Document 1] Japanese Patent Kokai Publication No. JP-P2007-208591A    [Patent Document 2] Japanese Patent Kohyo Publication No. JP-P2007-503186A    [Patent Document 3] Japanese Patent Kohyo Publication No. JP-P2007-506317A
The disclosures of the above Patent Documents 1 to 3 are incorporated herein by reference thereto.
The following gives the analysis of the related technology of the present invention.
In a WDM system, two types of transponders are used, one for a transmission/reception end and the other for regenerative repeating. This means that separate transponders must be prepared for use in exchanging transponders when a transponder fails. Another problem is that, once a predetermined wavelength and an incoming/outgoing path for a transmission/reception route are set up for a transponder, the setting cannot be remotely changed to the setting for another usage condition. Therefore, building a new optical path requires onsite installation work.
In the configuration disclosed in Patent Document 1 where the path switching and usage wavelength setting are variably controlled by an instruction from the network management apparatus, dedicated transponders are provided for regenerative repeating and add/drop multiplexing. In the configuration disclosed in Patent Document 2, the optical switches installed externally to a transponder, which are controlled by optical signals, are costly. In the configuration disclosed in Patent Document 3, the transponder does not have the line termination function.